Coding Resiliently with Akka

ResilientlyCoding

Scalain AkkawithDerek Wyatt

Twitter: @derekwyattEmail: [email protected]

Tuesday, 4 February, 14

mailto:[email protected]


What’s Resiliency?


What’s Resiliency?Tolerance against faultsW



Grace in the face of insane success W




Slowing down instead of shutting downW




Slowing down instead of shutting downW

to the crap that happensResiliency is about reactingbecause life is, basically a problem


CCCloud Resiliency


CCCloud ResiliencyCQueues

CClustered DatabasesCVirtual Machines

CZookeeperCLoad Balancers


CCCloud ResiliencyCQueues

CClustered DatabasesCVirtual Machines

CZookeeperCLoad Balancers

Great tools. I’m going to

assume you use them.


How Akka Helps


How Akka HelpsAkka is a toolki for asynchrony5Resilient systems are asynchronous systems



Akka is buil using queues5Queues add resilient points of communication




Akka divorces threads from work5Improper use of threads kills resiliency





Akka’s Actors incorporate faul tolerance5A crash is just standard operating procedure






Akka Clusters5Clustering? Come on... Resilient






Akka Clusters5Clustering? Come on... Resilient

And there’s more!


Why We Don’t Code Resiliently


Why We Don’t Code Resilientlya.k.a Callback Hell1) REST request comes in2) Validate user identity3) Get profile from DB4) Grab a few pics5) Get recent Twitter activity6) Return REST response



Do it asynchronously

and don’t block



Do it asynchronously

and don’t block

Welcome to Callback Hell


Callback Hell


Callback Hellpublic void restHandler(RESTRequest req) { idService.validate(req.userInfo, new Callback(ValidateResult result) { if (result.isValid) { db.getProfile(req.userId, new Callback(UserProfile profile) { picServer.get(profile.pic1, new Callback(Pic p1) { picServer.get(profile.pic2, new Callback(Pic p2) { picServer.get(profile.pic3, new Callback(Pic p3) { picServer.get(profile.pic4, new Callback(Pic p4) { picServer.get(profile.pic5, new Callback(Pic p5) { twitterServer.getRecentActivity(req.userInfo, new Callback(TwitterActivity activity) { req.sendResponse(pic1, pic2, pic3, pic4, pic5, activity) }) }) }) }) }) }) }) })}


Callback Hellpublic void restHandler(RESTRequest req) { idService.validate(req.userInfo, new Callback(ValidateResult result) { if (result.isValid) { db.getProfile(req.userId, new Callback(UserProfile profile) { picServer.get(profile.pic1, new Callback(Pic p1) { picServer.get(profile.pic2, new Callback(Pic p2) { picServer.get(profile.pic3, new Callback(Pic p3) { picServer.get(profile.pic4, new Callback(Pic p4) { picServer.get(profile.pic5, new Callback(Pic p5) { twitterServer.getRecentActivity(req.userInfo, new Callback(TwitterActivity activity) { req.sendResponse(pic1, pic2, pic3, pic4, pic5, activity) }) }) }) }) }) }) }) })}

We didn’t handle timeouts

We didn’t handle errors

We actually didn’t make it thread safe

We did throw up a little though...

☉☉☉☉


Functional Asynchrony


Functional Asynchronyimplicit val timeout = Timeout(30.seconds)def restHandler(req: RESTRequest): Future[RESTResponse] = { val resp = for { validity <- idService.validate(req.userInfo) if validity.isValid profile <- db.getProfile(req.userId) pic1 <- picServer.get(profile.pic1) pic2 <- picServer.get(profile.pic2) pic3 <- picServer.get(profile.pic3) pic4 <- picServer.get(profile.pic4) pic5 <- picServer.get(profile.pic5) activity <- twitterServer.getRecentActivity(req.userInfo) } yield SuccessfulResponse(pic1, pic2, pic3, pic4, pic5, activity) resp.recover { e => FailedResponse(e) }}


Functional Asynchronyimplicit val timeout = Timeout(30.seconds)def restHandler(req: RESTRequest): Future[RESTResponse] = { val resp = for { validity <- idService.validate(req.userInfo) if validity.isValid profile <- db.getProfile(req.userId) pic1 <- picServer.get(profile.pic1) pic2 <- picServer.get(profile.pic2) pic3 <- picServer.get(profile.pic3) pic4 <- picServer.get(profile.pic4) pic5 <- picServer.get(profile.pic5) activity <- twitterServer.getRecentActivity(req.userInfo) } yield SuccessfulResponse(pic1, pic2, pic3, pic4, pic5, activity) resp.recover { e => FailedResponse(e) }}

We handle timeouts (!!)

We handle errors (!!)

It’s immutable and thread safe (!!)

We got to keep our lunch down

☉☉☉☉


The Circuit Breaker


The Circuit BreakerFor the times when you gotta fail the whale ⦿



Closed

Open

HalfOpen

Success

Trip Breaker

Calls Failing Fast

Attempt Reset

Trip Breaker

Reset Breaker



Closed

Open

HalfOpen

Success

Trip Breaker

Calls Failing Fast

Attempt Reset

Trip Breaker

Reset BreakerDB



Closed

Open

HalfOpen

Success

Trip Breaker

Calls Failing Fast

Attempt Reset

Trip Breaker

Reset BreakerDB

Circuit Closed

Circuit Open


Load BalancingActors are untyped endpointsYou can easily swap one for anotherActors have dispatchersHow messages are dispatched is configurableYou can only communicate through messagesYou can route them however you like

Messages can carry the state dataActors then become completely stateless and Resilient


Scaling Up


Scaling Up⦿ It’s all about dispatchers and untyped endpoints


Scaling Up⦿ It’s all about dispatchers and untyped endpoints

••

Acto

rRef

Acto

rRef

Acto

rRef

BalancingDispatcher

Actor

Actor

Actor

Client

Normally the message from the client would go to the middle Actor, but the Balancing Dispatcher lets the last one “steal” it because it can handle it faster.


Scaling Out


Scaling Out☉Routers are another way for messages to reach Actors



☉A router igures ou which Actor to send to based on rules




DBActor

DBActor

Client Router DBActor

DB ClusterMachine 1

DB ClusterMachine 2

DB ClusterMachine 3




DBActor

DBActor


DB ClusterMachine 1

DB ClusterMachine 2

DB ClusterMachine 3

This router can

route consistently

based on sender




DBActor

DBActor


DB ClusterMachine 1

DB ClusterMachine 2

DB ClusterMachine 3

This router can

route consistently

based on sender

☉Routers can also resize the number o Actors dynamically


Clustering


Clustering

⦿Akka can spawn and communicate with Actors on remote nodes


Clustering

⦿Akka can spawn and communicate with Actors on remote nodes Boring!


Clustering

⦿Akka can spawn and communicate with Actors on remote nodes Boring! (OK, that’s really cool, but...)


Clustering


⦿ You can cluster your Actors as well


Clustering



⦿Akka takes care of letting you know when nodes come and go


Clustering



⦿Akka takes care of letting you know when nodes come and go

⦿Clustering provides a ton of possibilities to design for resiliency


Persistence - Event Sourcing


Persistence - Event Sourcing⨂ Akka provides the ability to persist incoming messages


Persistence - Event Sourcing⨂ Akka provides the ability to persist incoming messages⨂ This helps for fault tolerance... DUH


Persistence - Event Sourcing⨂ Akka provides the ability to persist incoming messages⨂ This helps for fault tolerance... DUH⨂ It also provides the ability to move stateful Actors


Persistence - Event Sourcing⨂ Akka provides the ability to persist incoming messages⨂ This helps for fault tolerance... DUH⨂ It also provides the ability to move stateful Actors⨂ Or provide tools for “Crash-Only” software

ActorMessageCrash! ActorEvent 1

Event 2

Event 3

Good to go!


Being Resilient


Being Resilient☉Akka provides the foundation for resilien programming and design

Queues, Dispatchers, Async, Messages, realistic guarantees⨳




☉Then you ge...

Routers⨳Clustering⨳

Remote Deployment⨳

Persistence⨳

Resiliency Patterns⨳

Message Oriented Flexibility⨳




☉Then you ge...



Persistence⨳



☉Existing cloud components are vial for resiliency




☉Then you ge...



Persistence⨳



☉Existing cloud components are vial for resiliency

☉Akka picks up where those components leave of


Go write some Code

http://akka.iohttp://github.com/akka/akka

http://scala-lang.orghttp://github.com/scala/scala

Get Scala

Get AkkaDerek Wyatt

Twitter: @derekwyattEmail: [email protected]


http://akka.io

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